The present invention relates to power and energy meters and, more particularly, to a simplified method of configuring a digital power or energy meter.
The total power consumption of a building or other facility is monitored by the electric utility with a power meter located between the utility's distribution transformer and the facility's power distribution panel. However, in many instances it is desirable to sub-meter or attribute the facility's power or energy usage and cost to different occupancies, buildings, departments, or cost centers within the facility or to monitor the power consumption of individual loads or groups of loads, such as motors, lighting, heating units, cooling units, etc. These single phase or multi-phase electrical loads are typically connected to one or more of the branch circuits that extend from the facility's power distribution panel.
Flexibility has favored adoption of digital power and energy meters incorporating data processing systems that can monitor one or more circuits and determine a number of parameters related to electricity consumption. A digital power or energy meter for measuring electricity consumption typically comprises one or more voltage and current transducers that are periodically read by the meter's data processing unit which, in a typical digital meter, comprises one or more microprocessors or digital signal processors (DSP). The data processing unit periodically reads and stores the outputs of the transducers quantifying the magnitudes of current and voltage samples and, using that data, calculates the current, voltage, power, and other electrical parameters, such as active power, apparent power and reactive power that quantify electricity distribution and consumption. The calculated parameters are typically output to a display for immediate viewing or transmitted from the meter's communications interface to another data processing system, such as a building management computer for remote display or further processing, for example formulating instructions to automated building equipment.
The voltage transducers of digital power and energy meters commonly comprise a voltage divider network that is connected to a conductor in which the voltage will be measured. The power distribution panel provides a convenient location for connecting the voltage transducers because typically each phase of the power is delivered to the power distribution panel on a separate bus bar and the voltage and phase is the same for all loads attached to the respective bus bar. Interconnection of a voltage transducer and the facility's wiring is facilitated by wiring connections in the power distribution panel, however, the voltage transducer(s) can be interconnected anywhere in the wiring that connects the supply and a load, including at the load's terminals.
The current transducers of digital power and energy meters typically comprise current transformers that encircle the respective power cables that connect the monitored circuit to the bus bar(s) of the distribution panel. A current transformer typically comprises multiple turns of wire wrapped around the cross-section of a toroidal core. The power cable conducting the load current is passed through the aperture in the center of the toroidal core and constitutes the primary winding of the transformer and the wire wrapped around the cross-section of the core comprises the transformer's secondary winding. Current flowing in the primary winding (primary current) induces a secondary voltage and current in the secondary winding which is quantitatively related to the current in the primary winding. The secondary winding is typically connected to a resistor network and the magnitude of the primary current is determined from the amplitude of the voltage at the output of the resistor network. To measure the power consumed by a load, a current transformer must be installed encircling each conductor in which the current will be measured.
While flexibility has made digital power and energy meters attractive, the ability to monitor a plurality of circuit arrangements conducting widely varying levels of energy complicates meter configuration increasing the time required for meter commissioning and the possibility of errors. What is desired, therefore, is a simplified method for configuring a power and energy meter.